Histology Lecture 5: Cell Cycle & Cell Division PDF

Histology lecture (5) Cell cycle & cell division Histology Cell cycle & Cell division Series of events that take place in a cell involving cell growth and cell Definition division and produce t...

Histology lecture (5) Cell cycle & cell division Histology Cell cycle & Cell division Series of events that take place in a cell involving cell growth and cell Definition division and produce two daughter cells. 1. Interphase (resting stage): Includes  Longest part of a cell’s life cycle & cell isn’t dividing. 2. Cell division. A Interphase (Resting Stage) Definition Period between 2 successive cell divisions. G1 (1st gap) stage. Includes S (synthesis) stage. G2 (2nd gap) stage. Histology G1 (1st gap) S (synthesis) G2 (2nd gap) stage stage stage Stage of s - Gap ( ) s stage & Gap ( ) end of mitosis & Def chromosome beginning of next beginning of (s) stage. duplication mitosis. Each identical pair of S- Growth of newly chromosomes form one formed daughter cell. DNA duplication Events d-chromosome. After growth: cells Duplication of pass to (S) centrioles. Number 46 of S-chrom 92 of S-chrom 46 of d-chrom Histology B Cell Division PHASES Karyokinesis Cytokinesis Nuclear division which divides the Cytoplasmic division. genetic material in nucleus. Types Mitosis Meiosis (indirect cell division) (reduction cell division) Somatic cells (all body cells Germ cells of testis & ovary Type of cells except eggs and sperms) No. of daughter Two daughter cells Four daughter cells cells No. of Same number of Half number of chromosomes in chromosomes as mother cell chromosomes of mother cell each daughter (46 schromosomes= (23 s chromosomes = cell diploid number) haploid Number) Histology 1 Mitosis Type of division in which there is production of two daughter cells, Definition each has same number of chromosomes as the mother cell (46 s - chromosomes). 1. Prophase. 2. Metaphase. Stages 3. Anaphase. 4. Telophase. Histology  Fragmentation of ER, Golgi and disassembly of cytoskeleton.  Mitotic spindle formation: Continuous microtubules arise ( ) pairs of centrioles (MTOCs) & grow gradually causing : a) Formation of eccentric spindle. b) Gradual elongation of cell.  Nuclear membrane breaks.  Nucleoli disintegrates  The spindle becomes central.  D-chromosomes lie in the inter-tubular spaces of spindle.  They become more condensed with appearance of kinetochores. Formation of chromosomal microtubules. d chromosomes: a) Become arranged at the cell equator b) Achieve the highest degree of condensation So, arresting this phase is ideal for karyotyping. Splitting of chromosomes at centromere (46 d chromosomes → 92 s chromosomes arranged in two identical sets ( 2 x 46 s chromosomes)). Separation: each set of s chromosomes move to the opposite pole of the cell, pulled by microtubules 1. Cytokinesis:  Formation of Contractile ring  Formation of cleavage furrow which deepens gradually until separation of the two daughter cells. 2. Nuclear envelope and nucleoli reappear. 3. The net result is the production of two daughter cells , each has 46 s chromosomes. Histology 2 Meiosis Type of division in which there is production of 4 cells, each one has Definition half (haploid) number of chromosomes (23 s - chromosomes). 1st Meiotic division Stages 2nd Meiotic division: the same as mitosis. NB No S stage in the interphase between both meiotic divisions. Histology Leptotene phase D-chromosomes appear as thin threads. Homologous d-chromosomes are paired with formation of Zygotene phase synaptonemal complex and called bivalents. Chromosomes condense and become thicker & shorter. Pachytene phase Crossing over occurs. Chromosomes are more condensed and appear as tetrad. Diplotene phase Chromosomes are separated except at chiasmata. Disappearance of nuclear envelope & nucleoli. Diakinesis Formation of the spindle. Histology 23 bivalent arranged in the cell equator. Sister chromatid attached by centromere. Non sister attached by chiasmata. longitudinal break at chaismata each set of 23 d chromosome migrate to opposite side. Cytokinesis result in formation of two cells each contain 23 d chromosome which surround by nuclear membrane to form nucleus Histology Prophase II Spindle is formed Metaphase II 23 d- chromosome arrange singly at cell equator Each d- chromosome splits into 2s- chromosome Anaphase II Each set of 23 s- chromosome move to opposite pole Telophase II Cytokinesis result in two cells each has haploid number 23 Histology Q Compare between mitosis & meiosis : Q Result of meiosis :  One cell gives 4 daughter cell.  Each cell contains 23 s chromosome (haploid cells).